This invention relates to enamine derivatives, processes for producing the same and electrophotographic plates containing the same as a charge transport material and excellent in sensitivity, photoresponse and durability.
In electrophotographic plates using photoconductive substances as a photosensitive material, there have been used mainly inorganic photoconductive substances such as selenium, zinc oxide, titanium oxide, cadmium sulfide, etc. But since most of these substances are generally strongly toxic, there is a problem in their disposal, otherwise they have low durability, e.g. in the case of zinc oxide.
On the other hand, photosensitive materials using organic photoconductive compounds are widely studied recently, since they are generally weak in toxicity and advantageous in transparency, flexibility, light-weight, cost, and the like comparing with the case of using the inorganic photoconductive substances.
Particularly in the case of two layers type electrophotographic plates wherein functions of generation and transport of charges are separated, the sensitivity which was a large defect of one layer type electrophotographic plates using organic photoconductive compounds can be improved greatly, so that the two layers type electrophotographic plates are rapidly progressing recently. These two layers type electrophotographic plates are applied to electrophotographic apparatuses by the Carlson method, e.g., copying machines, laser beam printers, facsimile machines, etc. With recent progress in miniaturization of electrophotographic apparatuses and high speed in printing speed, there have been demanded for electrophotographic plates so-called high speed photoresponse, wherein a surface potential at the time of exposing to a light image decays in a short time, and a longer life of printed copies.
The high speed photoresponse and the longer life are explained in detail below. With miniaturization of the electrophotographic apparatus, the diameter of a photoreceptive drum used in the apparatus becomes smaller. For example, the diameter of photosensitive drum in a large-size apparatus is 100 to 300 mm, while that in a small-size apparatus is 30 to 60 mm. Thus, in the small-size apparatus, individual parts such as a charging device, a developing device, etc. around the photoreceptive drum are installed in a narrow space and a time required for from the exposure to light image to the development is shortened compared with middle-size and large-size machines. Further, when the drum diameter is small, it is necessary to increase the revolving rate of drum in order to copy or print on sheets with the same rate. Therefore, in an electrophotographic process the time required for each step in an electrophotographic process of charging.fwdarw.exposing to a light image.fwdarw.developing.fwdarw.transferring.fwdarw.destaticizing becomes shorter and shorter. Further, among required performance for the electrophotographic plates, it becomes important to decay the surface potential rapidly after exposure to a light image. In other words, it is necessary to obtain electrophotographic plates good in photoresponse.
Further, since the drum diameter is reduced and the revolving rate is increased, it is necessary to repeat the above-mentioned electrophotographic process much more times compared with the case of using a larger drum diameter in order to obtain the same number of sheets by electrophotography. Thus, it is necessary to improve durability for repeated use of the electrophotographic plates.
The organic photosensitive body generally comprises a charge generating material which generates charges by absorbing light, a charge transport material which transports the charges, a binder and a small amount of additives depending on necessity. The photoresponse is mainly controlled by the charge transport material. In order to obtain high speed photoresponse, it is known to select suitable charge transport materials, or to increase the compounding ratio of the charge transport material to the binder.
As the charge transport materials, there are known pyrazoline derivatives disclosed in e.g. J. Photographic Science and Engineering vol. 21(2), p.73 (1977), etc.; oxazole derivatives disclosed in e.g. Japanese Patent Unexamined Publication No. 58-87557, U.S. Pat. Nos. 4,346,157; 4,619,879; 4,150,987; 4,278,747; 4,367,273; 4,365,014 and 4,454,212; hydrazone derivatives disclosed in e.g. Japanese Patent Unexamined Publication Nos. 54-59143, 54-150128 and 55-46760; enamine derivatives disclosed in e.g. J. Imaging Science vol. 29(1), p. 7 (1985); etc.
As to the method for enlarging the compounding ratio of the charge transport material to the binder in order to obtain high speed photoresponse, there are problems in known charge transport materials. For example, in the case of using pyrazoline derivatives and oxazole derivatives, the photoresponse is improved by increasing the compounding ratio of the charge transport material to the binder, but durability for repeated electrophotographic process is lowered, and there take place phenomena that an image fine line is broadened in the case of regular development and an image fine line is thinned in the case of reverse development. Such phenomena are called as lowering in print resolution. In the case of using hydrazone derivatives as the charge transport material, the photoresponse is undesirably slow, and there take place undesirably image fogging (toners are adhered to a white ground to make black) in the case of regular development and lowering in print density in the case of reverse development, due to an increase of potential after exposure to a light image, that is, an increase of residual potential, when electrophotography is repeated.
On the other hand, according to the above-mentioned J. Imaging Science, the following enamine derivatives are disclosed: ##STR1##
Among the compounds, it is described that the compounds (A), (B) and (C) are lacking in photoconductivity, the compound (D) is poor in photoconductivity and the compounds (E), (F) and (G) have good or excellent photoconductivity. But when the compounds (E), (F) and (G) are used as a charge transport material, they can withstand the repeated use but are insufficient in the sensitivity and photoresponse. The improvement in these points has been desired.